1. Field of the Invention
The invention relates to a vehicle and a driving method thereof, and more particularly relates to an electric power assist device adapted for an electric vehicle and a driving method for the electric vehicle to provide the electric vehicle with sufficient power on an uphill road.
2. Description of Related Art
A bicycle is a vehicle that is driven by manpower and does not consume any fossil energy. Due to energy shortage crisis, etc., many manufacturers begin producing electric bicycles by adding electric motors, batteries, etc. onto bicycles for driving the bicycles by electric power. Some types of electric bicycles are still equipped with pedals to allow the user to select whether to ride the bicycle by manpower or by electric power. On the other hand, some other types of electric bicycles are similar to motorcycles and do not have any pedal. Those electric bicycles are driven by electric power instead of fossil energy (such as gasoline).
According to the traffic regulations in most of the countries, electric bicycles are categorized as low-speed vehicles. Since it may be difficult to put a restriction on the age of electric bicycle users, most countries restrict the maximum speed of electric bicycles by laws in order to reduce the occurrence of traffic accidents, which also limits the weights of the electric bicycles or the output power of its electric motors. However, when the user rides the electric bicycle on an uphill road, insufficient output power of the electric motor may seriously affect the riding of the electric bicycle or electric vehicle. On the contrary, when the user rides the electric bicycle downhill, the speed may become too fast to brake, which may be dangerous for the user.
Therefore, how to provide sufficient power output when the electric bicycle is ridden uphill and how to maintain stability and safety when the electric bicycle is ridden on level or downhill road are important issues that need to be solved.